media gateway control and the softswitch architectureacpang/course/voip_2004/slides/chap6... · n...
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2IP Telephony
Outline
n Introductionn Softswitch
n Softswitch Architecturen Softswitch Operations
n Media Gateway Control Protocolsn MGCPn MEGACO
3IP Telephony
Next Generation Network
n Internet Telecom & Wireless Communication
IP
MGCF
CSCF
T-SGW MGWMGW
WLAN
GPRS
CSCFSIP
Server
PSTN
InternetWireless App.Server
3rd Parties App.
4IP Telephony
Gateways in Next Generation Networks
MGC : Media Gateway ControllerSG : Signaling GatewayTGW : Trunking GatewayRGW : Residential Gateway
CO
SCP
STP
PBX
H.323GK
SS7/IN
PSTN IP Networks
SG
TGW
H.323MG
MGC
MGCP/MEGACOH.323/SIPSIGTRANRTP/RTCP
Analog Line
TrunkMGCP/MEGACO
PhonesRGW
H.323 Phones
5IP Telephony
H323, SIP & MGCP, MEGACO
GWGK
MCU
GW : GatewayGK : GatekeeperTN : TerminalMCU : Multipoint Control Unit
TN
PSTN CA
TGW RGW
CA : Call AgentTGW : Trunking GatewayRGW : Residential GatewaySG : Singling Gateway
SS7
PSTN CO
SG
RTP
MGCP
H.323
TNTN
GWGK
MCU
TN
TNTN
6IP Telephony
H323, SIP & MGCP/MEGACO
n H.323 , SIPn peer-to-peern internet orientedn intelligent endpoint
n optional GK n decentralized
n Problemsn maintenance
n cost & scalability of large systems
n signaling & media control are coupled
n interoperability with SS7
n MGCP/MEGACOn client-servern traditional telephonyn intelligent server
n “dumb” terminaln centralized
n Conceptn gateway decomposed
n separate call control from media ports
n CA (MGC), MG, SGn interoperability with
PSTN
7IP Telephony
Class 5 End Office Switch
The Telephone Network [1/2]
Circuit Switched Network
Intelligent Peripheral
Signal Transfer Point
Service Control Point
Class 4 Tandem Switch
Service Data Point
+
Transport Layer
Control Layer
SS7 SignalingISUP MessagesINAP/TCAP Messages
8IP Telephony
The Telephone Network [2/2]
n 5 Basic Components in Intelligent Networksn SSP/Service Switching Point
n switching, signaling, routing, service invocation
n STP/Service Transfer Pointn signaling, routing
n SCP/Service Control Pointn service logic execution
n SDP/Service Data Pointn subscriber data storage, access
n IP/Intelligent Peripheraln resources such as customized voice announcement,
voice recognition, DTMF digit collection
SSPSSP
SCPSCP SDPSDP
STPSTPIPIP
SSPSSP
STPSTP
TCAP messages
ISUP messages
Voice
9IP Telephony
Softswitch
n The switching functions are handled by software
n International Softswitch Consortium (ISC)n www.softswitch.orgn To promote the softswitch concept and related
technologies
n Why the softswitch approach is popular?n A distributed architecturen For network operators
n It is possible to use different network components from different vendors.
n For equipment vendorsn It is possible to focus on one area.
11IP Telephony
Softswitch/PSTN Interworking
n SIP is often used as the signaling protocol between the MGCs.
Mo d em Ban k
12IP Telephony
Softswitch Overview [1/3]
n Softswitch: Emulating Circuit Switching in Software
IN/SCPPSTNLocal Switch
PSTNLocal Switch
STP SS7 Network
IP Network
RTP Streams
MGCMGC MGCMGC
Trunk Trunk GatewayGateway
Trunk Trunk GatewayGateway
SIP-T
SGSGSGSG
SIGTRAN
MEGACO
IP PhoneIP Phone
90009000 Personalized VoIPService System
Application ServerApplication Server
13IP Telephony
Softswitch Overview [2/3]
n Softswitch Provides Open Layered Architecture
• Solutions in a proprietary box• Expensive• Little room for innovation
Circuit-Switched
TransportHardware
Call Control & Switching
Services & Applications
PROPRIETARY
• Solutions are open standards-based• Customers choose best-in-class products • Open standards enable lower cost for
innovation
Soft-Switched
Transport Hardware
Softswitch Call Control
Services, Applications & Features (Management,
Provisioning and Back Office)
Open Protocols APIs
Open Protocols APIs
Open APIs for 3rd Party App develop.
Best-in-class Access Devices.
Scalable, Open Interfaces for Comm.
14IP Telephony
Softswitch Overview [3/3]
n Softswitch Changes the Telecom Landscapen Integration/Incorporation
n Convergence of voice and datan Combination of telecom & internet technologiesn Reuse PSTN database & IN services in packet networks n Multiple sources for app development & deploymentn Decreased operating costs
n Standardizationn Standard interfaces (protocols) for communicationsn Open standards (APIs) for service creationn Customized services created by users themselvesn Better scalability
15IP Telephony
Softswitch Architecture
COSwitch
STP
SCP
COSwitch
STP
SCP
Signaling Layer
Transport Layer
IP
SIP-T
MediaServer
RTP
SIP-?/MGCP
SIP-TSI
Media Gateway
Controller
MGCP/MEGACOPhones
App.Server
Media Gateway
Controller
SIGTRANSSA/SCTP
MGCP/MEGACOTrunkingGateway
Signaling(SS7)
Gateway
SS7 TCAP
ISUP/TCAP
16IP Telephony
LocalSwitch
STP
SCP
STP STP STP
LocalSwitch
STP
LocalSwitch
TrunkingGateway
Signaling(SS7)
GatewayMedia
GatewayController
TrunkingGateway
Signaling(SS7)
Gateway
RoutingDirectory
Softswitch Operations [1/3]
n Basic Call Control
12 ISUP ACM13 ISUP
ANM
ISUP ACMISUP ANM
ISUP IAM ISUP IAM
1
23
4 5
6 7
8
910
14
11
SIGTRAN
MGCP/MEGACOVoice Voice
RTP
17IP Telephony
Softswitch Operations [2/3]
n Inter-Softswitch Communications
LocalSwitch
STP
TrunkingGateway
Signaling(SS7)
GatewayMedia
GatewayController
STP
TrunkingGateway
STP
MediaGateway
Controller
Signaling(SS7)
Gateway
STP STP
Domain A Domain B
LocalSwitch
RoutingDirectory
3
1
5
2
ISUP IAM
4
SIGTRAN
MGCP/MEGACO
6 SIP-T
7
9
16
Voice
RTP
8
ISUP IAM
12
13
Voice
10
11
14 ISUP ACM15 ISUP
ANM
ISUP ACMISUP ANM
18IP Telephony
Softswitch Operations [3/3]
n IP-PSTN Interworking for IN Services
LocalSwitch
STP
SCP
STP STP STP
LocalSwitch
STP
LocalSwitch
TrunkingGateway
Signaling(SS7)
GatewayMedia
GatewayController
TrunkingGateway
Signaling(SS7)
Gateway
RoutingDirectory
ISUP IAM ISUP IAM
1
23
4
7
8 9
10
1112
13
SIGTRAN
MGCP/MEGACOVoice Voice
RTP
5
INAP/TCAP
16
6
14 ISUP ACM15 ISUP
ANM
ISUP ACMISUP ANM
19IP Telephony
Introduction
n Voice over IPn Lower cost of network implementationn Integration of voice and data applicationsn New service featuresn Reduced bandwidth
n Replacing all traditional circuit-switched networks is not feasible.
n VoIP and circuit-switching networks coexistn Interoperationn Seamless interworking
20IP Telephony
Separation of Media and Call Control
n Gatewaysn Interworkingn To make the VoIP network appear to the circuit
switched network as a native circuit-switched system and vice versa
n Signaling path and media path are different in VoIP systems.n Media – directly (end-to-end)n Signaling – through H.323 gatekeepers (or SIP
proxies)n SS7, Signaling System 7
n The logical separation of signaling and media
21IP Telephony
Separation of Media and Call Control
n A network gateway has two related but separate functions.n Signaling conversion
n The call-control entities use signaling to communicate.
n Media conversionn A slave function (mastered by call-control entities)
n Figure 6-1 illustrates the separation of call control and signaling from the media path.
22IP Telephony
Separation of Media and Call Control
n Advantages of Separationn Media conversion close to the traffic source and
sinkn The call-handling functions is centralized.n A call agent (media gateway controller - MGC) can
control multiple gateways.n New features can be added more quickly.
n MGCP, Media Gateway Control Protocoln IETF
n MEGACO/H.248n IETF and ITU-T Study Group 16
23IP Telephony
Requirements for Media Gateway Control [1/2]
n RFC 2895n Media Gateway Control Protocol Architecture and
Requirementsn Requirement
n The creation, modification and deletion of media streamsn Including the capability to negotiate the media formats
n The specification of the transformations applied to media streams
n Request the MG to report the occurrence of specified events within the media streams, and the corresponding actions
24IP Telephony
Requirements for Media Gateway Control [2/2]
n Request the MG to apply tones or announcementsn The establishment of media streams according to
certain QoS requirementsn Reporting QoS and billing/accounting statistics
from an MG to an MGCn The management of associations between an MG
and an MGCn In the case of failure of a primary MGC
n A flexible and scalable architecture in which an MGC can control different MGs
n Facilitate the independent upgrade of MGs and MGCs
25IP Telephony
Protocols for Media Gateway Controln The first protocol is MGCP
n RFC 2705, informationaln To be succeeded by MEGACO/H.248n Has be included in several product developments
n MEGACO/H.248n A standards-track protocoln RFC 3015 is now the official version.
IPDC
SGCP
MGCP
MDCP
MEGACO
Telcodia (Bellcore)
Level 3 Communication
Lucent (by ITU-T)
IETF RFC 3015ITU-T H.248November 2000
IETF RFC 2705October 1999
MGCP 1.0
IETF RFC 3435January 2003
27IP Telephony
MGCP/MEGACOPhones
TrunkingGateway
SignalingGateway
MGC
SIGTRANSSA/SCTP
RTP
MGCP/MEGACO
SS7 TCAP
ISUP/TCAP
Concept of MGCP/MEGACO
COSwitch
STP
SCP
PSTNPhones
Media Gateway
MGC
ConnectionCreateDeleteModify
Event NotificationRequest
StatusQuery
ResponseSuccessFailure
EventNotify
StatusReport
Dumb ClientStateless
Intelligent Server
28IP Telephony
MGCP
n A master-slave protocol (A protocol for controlling media gateways)n Call agents (MGCs) control the operation of MGs
n Call-control intelligencen Related call signaling
n MGsn Do what the CA instructsn A line or trunk on circuit-switched side to an RTP port on the IP
side
n Types of Media Gatewayn Trunking Gateway to CO/Switchesn Residential Gateway to PSTN Phonesn Access Gateway to analog/digital PBX
n Communication between call agentsn Likely to be the SIP
29IP Telephony
The MGCP Model
n Endpointsn Sources or sinks of median Trunk interfacesn POTS line interfacesn Announcement endpoint
n Connectionsn Allocation of IP resources to an endpointn An ad hoc relationship is established from a
circuited-switched line and an RTP port on the IP side.
n A single endpoint can have several connections
30IP Telephony
MGCP Endpoints [1/3]
n DS0 channeln A digital channel operates at 64kbps.n Multiplexed within a larger transmission facility
such as DS1 (1.544 Mbps) or E1 (2.048 Mbps)n G.711 (u-law or A-law)
n Analog linen To a standard telephone linen An analog voice streamn Could also be audio-encoded data from a modem
n The gateway shall be required to extract the data and forward it as IP packets.
31IP Telephony
n Announcement server access pointn Provide access to a single announcementn One-way
n No external circuit-switched channels
n Interactive voice response (IVR) access pointn Provide access to an IVR system
n Conference bridge access pointn Media streams from multiple callers can be mixed
n Packet relayn A firewall between an open and a protected
networks
MGCP Endpoints [2/3]
32IP Telephony
MGCP Endpoints [3/3]
n Wiretap access pointn For listening to the media transmittedn One way
n ATM trunk-side interfacen The termination of an ATM trunkn May be an ATM virtual circuit
33IP Telephony
n GW’s Domain Name + Local Name n Local Name
n A hierarchical form: X/Y/Z
n trunk4/12/[email protected] To identify DS0 number 7 within DS1 number 12 on DS3
number 4 at gateway.somenetwork.net
n Wild-cardsn $, any; *, alln e.g., trunk1/5/[email protected]
n CA wants to create a connection on an endpoint in a gateway and does not really care which endpoint is used.
n e.g., trunk1/5/*@gateway.somenetwork.netn CA requests statistical information related to all endpoints on
a gateway.
Endpoint Identifier
34IP Telephony
MGCP Calls and Connections
n A connectionn Relationship established between a given endpoint and an
RTP/IP sessionn A call
n A group of connectionsn The primary function of MGCP is to enable
n The connections to be createdn The session descriptions to be exchanged between the
connections
1 2 3
4 5 6
7 8 9
* 8 #
1 2 3
4 5 6
7 8 9
* 8 #
35IP Telephony
n Call Identifier (Call ID)n Created by CAn Unique within CA Scope
n Connection ID n Created by GWn Unique under Its GW
n CA Identifier (its domain name)n Redundant CAs with a domain name: reliability
Calls, Connections and Call Agents
Endpoint Endpoint
CA1. CRCX3. MDCX
2. CRCX
IP, Port, Packetization
RTP
36IP Telephony
n 9 commands to handle Connection/Endpointsn EndpointConfiguration (coding characteristics)n NotificationRequest (requested events)n Notify (GW: detected events)n CreateConnectionn ModifyConnectionn DeleteConnectionn AuditEndpointn AuditConnectionn RestartInProgress (GW : taken in/out of service)
n All commands are acknowledged.
EPCF RQNTNTFYCRCXMDCXDLCXAUEPAUCXRSIP
MGCP Commands
37IP Telephony
MGCP Command Format
n A command linen Request verb (the name of the command)n Transaction id n Endpoint id (for which the command applies)n Protocol version
n A number of parameter linesn An optional session description (SDP)
n Separated by a single empty line
n Command Encapsulationn One command can be included within anothern Only one level of encapsulationn E.g., when instructing a gateway to create a connection, CA
can simultaneously instruct the gateway to notify the CA of certain events.
38IP Telephony
MGCP Parameters [1/6]
n BearInformation (B)n The line-side encodingn B:e:mu
n CallId (C)n Comprised of hexadecimal digits
n Capabilities (A)n In response to an audit
n ConnectionId (I)n Comprised of hexadecimal digits
n ConnectionMode (M)n Send only, receive only and send-receive
39IP Telephony
MGCP Parameters [2/6]
n ConnectionParameters (P)n Connection-related statistical informationn Average latency, jitter, packets sent/received/lostn GW -> CA
n DetectEvents (T)n That an endpoint should detect during quarantine periodn E.g., off-hook, on-hook, hook-flash, DTMF digits…
n LocalConnectionDescripter (LC)n An SDP session description
n LocalConnectionOptions (L)n Bandwidth, packetization period, silence suppression, gain
control, echo cancellation…n L: e:off, s:on
n To turn echo cancellation off and to turn silence suppression on
40IP Telephony
MGCP Parameters [3/6]
n EventStates (ES)n In response to an audit commandn A list of events associated with the current state
n MaxMGCPDatagram (MD)n To indicate the maximum size MGCP packet supported by
an MGn Included in the response to an AUEP command
n NotifiedEntity (N)n An address for the CA
n ObservedEvents (O)n Detected by an endpoint
n PackageList (PL)n Supported by an endpointn Events and signals are grouped into packages
n Analog line endpoint
41IP Telephony
n Events & Signalsn package name(o)/event or signal name (insensitive)
n L/hu = Hu (if L is the default package for the endpoint)
n packages: grouping of events & signals for a particular type of endpointsn Generic Media (G)n DTMF (D)n MF (M)n Trunk (T)n Line (L)n Handset (H)n RTP (R)n Script n Network Access Server (N)n Announcement Server (A)
n The experimental packages have names beginning with the two character “x-”.
MGCP Packages
Gateway Supported packages
Trunk GW (ISUP)Trunk GW (MF)Network Access ServerCombined NAS/VOIP GWAccess GW (VOIP)Access GW (VOIP + NAS)Residential GWAnnouncement GW
G, D, T, RG, M, D, T, RG, M, T, NG, M, D, T, N, RG, M, D, RG, M, D, N, RG, D, L, RA, R
42IP Telephony
MGCP Parameters [4/6]
n QuarantineHandling (Q)n Events that occur during the
period in which the GW is waiting for a response to a Notify command
n Process the events or discard them
n ReasonCode (E)n When a GW deletes/restarts a
connection
n RemoteConnectionDescripter(RC)n An SDP session description
Q: process/discardstep/loop (notify)
T: events to detect during quarantine
Q: process/discardstep/loop (notify)
T: events to detect during quarantine
Request Response
Time
Quarantine Period
Notify
43IP Telephony
MGCP Parameters [5/6]
n RequestEvents (R)n A list of events that an endpoint is to watch forn Associated with each event, the endpoint can be instructed
to perform actionsn E.g., collect digits, or apply a signal
n RequestInfo (F)n In response to audit requestsn The current values of RequestEvents, DigitMap,
NotifiedEntity
n RequestIdentifier (X)n To correlate a given notification from a GW
n RestartDelay (RD)n A number of seconds indicating when an endpoint will be
brought back into service
44IP Telephony
MGCP Parameters [6/6]
n RestartMethod (RM)n Graceful or Forced
n SecondConnectionId (I2)n The connection on a second endpoint
n SecondEndpointID (Z2)n A connection between two endpoints on the same
GWn SignalRequests (S)
n Signals to be applied by an endpoint
n SpecificEndpointID (Z)n Used to indicate a single endpoint
45IP Telephony
Inter-digit Timer
n CA ask GW to collect user dialed digitsn Created by CA
n Usagen Gateways detect a set of digits.
n e.g., (11x|080xxxxxx|03xxxxxxx|002x.T)
n Match accumulated digitsn under-qualified, do nothing furthern matched, send the collected digits to CAn over-qualified, send the digits to CA
Digit Map
46IP Telephony
MGCP Response
n Headern A response linen Return code + TransID + Commentaryn A set of parameter lines (optional)
n E.g., I: A3C47F21456789F0 (ConnectionId)
n Session Descriptionn Session Description Protocoln separated from header by an empty line
47IP Telephony
Return Code
n 100~199: provisional responsen current being executed
n 200~299: successful completionn executed normally
n 400~499: transient errorn could not be executed because of no sufficient
resources at this timen phone already off/on hook
n 500~599: permanent errorn endpoint unknownn protocol error
48IP Telephony
Protocol Description [1/2]
n Transactions (simple text format)n command
n headern a command line (case insensitive)
n Action + TransId + Endpoint + Version n a set of parameter lines
n parameter name (upper case): valuen Example
n RQNT 1201 endpoint/[email protected] MGCP 1.0n X: 0123456789B1 (RequestIdentifier) n R: hd (requestedEvent: hang down)n S: rg (signalRequest: ring tone)
n session description
49IP Telephony
Protocol Description [2/2]
n Transactionsn response
n headern a response line
n Response code + TransId + Commentaryn a set of parameter lines (optional) n Example
n 200 1201 OKn after CRCX(/MDCX/DLCX/Audit/Restart)n I: A3C47F21456789F0 (ConnectionId)
n session descriptionn Session Description Protocol (RFC 2327)n separated from header by an empty line